This invention relates to an improved sealing arrangement for an encapsulated measuring system for measuring the position of first and second objects movable with respect to one another, of the type which includes a housing adapted to be connected to the first object, which housing defines a slit extending along the measuring direction, a scanning unit disposed in the housing, and a follower, adapted to be connected to the second object and coupled to the scanning unit to extend through the slit.
A wide variety of such measuring systems are known to the art. By way the example, German Patent DE-PS No. 26 23 526 discloses an example of a length measuring system of this type.
In this system the sealing lips which close the slit in the housing are arranged in a roof form and are formed of an elastic synthetic material. The sealing lips abut one another with a sealing effect in order to seal the interior of the housing. The sealing lips are spread apart in a limited region where the follower extends between the sealing lips in order to conform to the contour of the follower. Such sealing is provided for measuring systems in order to prevent harmful environmental influences from damaging or interfering with the operation of measuring of components arranged in the interior of the housing.
Often, when such measuring systems are installed on machine tools, the measuring systems come into contact with fluids such as coolants and lubricants that must be kept out of the interior of the measuring device by the sealing lips. Such fluids can attack the material of which the sealing lips are formed, thereby causing the sealing lips to swell so that their length changes. In addition, some of the fluids are sufficiently aggressive to adversely alter the sliding or frictional properties of the sealing lips.
In the event aggressive fluids present in the machine tool environment cause the sealing lips to swell, the lips tend to dispose themselves in an undulating pattern which causes the sealing properties of the sealing lips to deteriorate. In some cases, the surface of the sealing lips may be attacked in such a way that the friction between the sealing lips and the follower becomes unacceptably high.